Apparatus for adapting a rifle to fire a different projectile

ABSTRACT

An adaptor for attachment to the end of a rifle allows an individual to  f from the rifle a different projectile than originally designed for the rifle, without substantial degredation in overall accuracy and throw distance of the rifle. The adaptor has a rifled cylinder which in the typical application will have progressive twist rifling. The tangential force acting upon the projectile within the progressive twist rifling area has a semi-elliptical shape and an exit value of approximately zero. An adaptor ring and outer shell are preferably employed to mount the rifled cylinder to the rifle and for aligning the adaptor axis and rifling with the rifle barrel axis and rifling.

GOVERNMENTAL RIGHTS

The invention described herein may be manufactured, used and licensed byor for the Government for Governmental purposes without the payment tome of any royalties thereon.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates in general to rifles and more particularlyto apparatus for adapting a rifle to fire a projectile of differentdesign than the rifle was manufactured to fire.

2. Background Information

Presently, the basic United States Army infantry rifle is the M-16 andthe cartridge designed to be fired from this rifle is the M-193. At thetime of the present invention, NATO, through its various technicalpanels and study commissions, was conducting a technical evaluationprogram to determine the best cartridge to be used in connection withits new Infantry Rifle Standardization Agreement. Among the candidatesfor selection was the Belgium SS-109 cartridge. Certain logistical andtechnical problems would have arised for the United States infantry ifthe SS-109 projectile had been selected as the desirable cartridge forthe standardization effort. Although the Belgium SS-109 and the U.S.M-193 share basically the same physical envelope, the projectile designsare sufficiently different that the SS-109 requires a higher spin rateto achieve gyroscopic stability than the M-193. If the Belgium SS-109 isfired from the standard U.S. M-16 rifle, problems of reducedeffectiveness at normal firing temperatures and total instability atreduced air temperatures occur, thus compromising the rifle'susefulness.

Should the Belgium SS-109 cartridge have been chosen for the NATOinfantry standardization effort then prompt cooperation by the UnitedStates Government would have meant replacing all existing M-16 rifleswith barrels having rifling characteristics like those of a Belgianrifle designed to fire the SS-109 cartridge, or designing an adaptorwhich could be field installed to provide the additional spin rateneeded to stablize the SS-109 projectile fired from the U.S. M-16. Thepresent is the result of extensive research involving this latteroption.

Previous attempts to design a similar adaptor for attachment to the endof a rifle have generally failed. These attempts have been unsuccessfulin maintaining gyroscopic stability of the projectile upon its exit fromthe adaptor, primarily because of continued projectile angularacceleration after the projectile has exited from the adaptor, aninherent result of the approach taken by these prior attempts.Projectile angular acceleration after the projectile has exited from theadaptor will cause the projectile to yaw or oscillate, thus reducing theoverall effectiveness of the weapon. This projectile angularacceleration results from the prior art use of an exponential functionto progressively change the rifle twist rate.

Therefore, there exists a genuine need for an effective, inexpensiveadaptor for attachment to the end of a rifle which will allow anindividual to fire from the rifle a projectile, different than theprojectile originally designed for the rifle, without substantialdegradation in the overall accuracy and throw distance of the rifle.

SUMMARY OF THE INVENTION

Briefly, the present invention satisfies this need by providing a spinamplifying adaptor for attachment to the end of the rifle; the adaptorbeing uniquely designed to substantially eliminate projectile angularacceleration after the projectile has exited the adaptor. The adaptorincludes a rifled cylinder which in the preferred implementation willhave progressive twist rifling. As a result of this progressive twistrifling there will be a tangential force acting upon the projectilewithin the rifled cylinder. In the preferred embodiment of the presentinvention, this tangential force will have a semi-elliptical shape whenplotted against distance along the rifled cylinder axis, with anentrance and exit value of approximately zero. The progressive twistrifling which will result in this tangential force has an instantaneoustwist rate which is a function of the longitudinal location of theprojectile within the rifled cylinder, the initial and final twist rateswithin the rifled cylinder, and the length of the progressive twistrifling area within the rifled cylinder. The projectile will bestabilized at a desired increased angular velocity upon exiting from theadaptor due to the approximately zero tangential force acting upon itjust prior to exiting from the rifled cylinder.

The preferred structural embodiment of the present invention includes arifled cylinder having the above described progressive twist rifling andeccentric inner and outer surfaces. Also provided is an outer shellhaving a specially designed bore at one end for receiving the rifledcylinder, and a second, shorter bore, at its opposite end, for receivingan adaptor ring. These two bores in the outer shell are designed to beaxially offset and longitudinally spaced from each other. The adaptorring will have a threaded inner surface for easy attachment to a riflebarrel which is ordinarily threaded on the end for receiving a flashsuppressor. The adaptor ring will ordinarily have eccentric inner andouter surfaces. The eccentricities, although slight, provide asufficient degree of freedom to properly align the adaptor axis andrifling with the rifle barrel axis and rifling. This freedom ofalignment is useful in accommodating the variations that result from thestandard practice of manufacturing rifle barrels within certainmeasurable tolerances. The adaptor may be locked onto the rifle barrelby placing a lock nut on the rifle barrel threads before attaching theadaptor ring. Set screws, used to secure the rifled cylinder, outershell and adaptor ring in a fixed relation, may be inserted throughthreaded holes in the outer shell to engage circumferentially cutgrooves in the rifled cylinder and adaptor ring. Optional threads may beincluded on the outer surface of a part of the rifled cylinderprojecting from the outer shell, for accommodating a flash suppressor.

A primary object of the present invention is the provision of an adaptorfor attachment to the end of a rifle which will allow an individual tofire from the rifle a projectile, different than the projectileoriginally designed for the rifle, without substantial degradation inthe overall accuracy and throw distance of the rifle.

Another object of the present invention is the provision of an adaptorfor attachment to the end of a rifle barrel which will provide spinamplification and gyroscopic stability to a projectile not originallydesigned to be fired from the rifle.

Yet another object of the present invention is the provision of a rifleadaptor having progressive twist rifling yet zero exit projectileangular acceleration.

A further object of the present invention is the provision of such arifle adaptor capable of attachment to the end of different riflebarrels manufactured within certain measurable parameters.

A still further object of the present invention is the provision of arelatively inexpensive and easy to construct rifle adaptor which can beeasily installed by an individual.

Still another object of the present invention is the provision of arifle adaptor capable of accommodating a flash suppressor on the endthereof.

Yet another object of the present invention is the provision of anadaptor for attachment to the end of a standard United States infantryM-16 rifle which will allow a Belgium SS-109 cartridge to be firedtherefrom without substantial degradation in rifle performance.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is an exploded, perspective view of the present invention showingthe principal components of its preferred structural embodiment.

FIG. 2 is a lengthwise cross-sectional view of the rifled cylinder ofthe present invention and

FIG. 2A is an end view of the rifled cylinder.

FIG. 3 is a graph of the typical loading caused by the adaptor, showingthe force, in pounds, acting upon the projectile and the twist rate ofthe projectile, in inches per turn, within the progressive twist riflingarea of the rifled cylinder.

FIG. 4 is a representation of one rifling groove within the rifledcylinder showing the generation in degrees within the progressive twistrifling area of the rifled cylinder.

FIG. 5 is a lengthwise cross-sectional view of the assembled adaptorattached to the end of the rifle barrel.

FIG. 6 is a lengthwise cross sectional view of the adaptor ring and

FIG. 6A is an end view of the adaptor ring.

FIG. 7 is a lengthwise cross-sectional view of the outer shell and

FIG. 7A is an end view of the outer shell, shown from the end designedto receive the rifled cylinder.

DETAILED DESCRIPTION OF THE INVENTION

The principal components of the preferred embodiment of the presentinvention, a rifled cylinder 10, an outer shell 12, and an adaptor ring14, all of which are discussed in detail below, are shown in an explodedview in FIG. 1.

A typical application of the present invention would be the use of theadaptor to provide gyroscopic stability to a projectile that is longerthan originally designed to be fired from a certain rifle. Gyroscopicstability of such a projectile may be obtained by increasing the angularvelocity of the projectile. Structurally central to accomplishing thisgoal of the present invention is the rifled cylinder 10, shown in alengthwise, cross-sectional view in FIG. 2. Generally, the rifledcylinder 10 may be rifled in such a way as to provide an increase, ordecrease, in angular velocity function. For the application describedabove, the rifled cylinder 10 will function to increase the angularvelocity of the projectile when the rifled cylinder 10 is manufacturedto have a progressive twist rifling area of length L on its innersurface 22. By selectively increasing the rifling twist rate, it ispossible to obtain a desired angular velocity for any given projectile.As a result of this progressive twist rifling area a tangential force isapplied to the projectile in such a way as to increase the angularvelocity of the projectile.

The adaptor of the present invention accomplishes the above describedbasic function of increasing projectile angular velocity while at thesame time substantially eliminating projectile angular accelerationafter the projectile has exited from the rifled cylinder 10. This isaccomplished by designing the rifled cylinder 10 in such a way thatthere is substantially no tangential force acting upon the projectilejust prior to its exiting the adaptor. As noted earlier, projectileangular acceleration subsequent to the projectile exiting the adaptorcauses the projectile to yaw or oscillate, reducing the overalleffectiveness of the weapon. The elimination of projectile angularacceleration from the projectile exiting from the adaptor has resultedin the present invention being the only rifle adaptor known to theinventor, which is capable of maintaining the gyroscopic stability of aprojectile fired from a rifle not originally designed to fire it througha wide temperature range.

Several mathematical functions were examined in the search for theoptimal tangential force equation upon which to pattern the progressivetwist rifling within the rifled cylinder 10. In choosing a desirabletangential force function it was also necessary to consider thedesirability of providing a substantially zero tangential force actingupon the projectile at the entrance to the rifled cylinder 10. Byslightly delaying the application of a tangential force to theprojectile within the rifled cylinder 10, it was possible to provide asmoother transition for the projectile 17 from the rifle barrel 16 (seeFIG. 5) to the rifled cylinder 10.

The preferred embodiment of the present invention is asemi-elliptically-shaped tangential force equation having a valueapproximately zero at both ends of the progressive twist rifling area.An elliptical expression for the tangential force was chosen for itsworkability and ultimate efficiency when applied within the rifledcylinder 10, although, at least theoretically, other mathematicalfunctions which have a value of approximately zero at each end andsufficient non-zero value therebetween might be employed. Afterselection of a semi-elliptically-shaped tangential force equation it waspossible to express the maximum force that the projectile wouldexperience within the progressive twist rifling area as follows:##EQU1## In this equation, I_(xx) is a shorthand representation for theaxial projectile moment of inertia, V is the longitudinal velocity ofthe projectile within the rifled cylinder, D is the projectile diameter,L is the length of the progressive twist rifling area of the rifledcylinder 10, N_(I) is the rifling twist rate at the entrance to therifled cylinder and N_(F) is the rifling twist rate at the exit of therifled cylinder. It will be observed that for a given implementation ofthe present invention, I_(xx), V, D, N_(I), and N_(F) are allindependently determinable quantities.

As noted in Equation 1, the maximum tangential force applied to theprojectile within the progressive twist rifling area is inverselyproportional to the length L of the progressive twist rifling area.Through independent stress analysis it is possible to determine themaximum tangential force that a projectile can withstand. The length Lof the gain twist rifling area may then be determined through theutilization of Equation 1 and the selection of an appropriate peaktangential force (i.e. a value below the maximum tangential force theprojectile can sustain). Note that the higher tangential force that aprojectile can withstand the shorter the progressive twist rifling arealength L is required.

An expression of the instantaneous rifling twist rate within theprogressive twist rifling area may be obtained by successivelyintegrating the tangential force equation, Equation 1, as is well knownin the art. The instantaneous rifling twist rate within the progressivetwist rifling area may then be expressed as the following: ##EQU2## Thenew variables in this second equation are N, the instantaneous riflingtwist rate; X, projectile travel distance within the progressive twistrifling area; and ASIN, the inverse sine. From Equation 2 it is possibleto calculate and plot the rifling generation within the rifled cylinder10 for the length of the progressive twist rifling area L. This isaccomplished by arbitrarily selecting a number of datum points, that is,values for X, and then calculating the instantaneous rifling twist rateN for those locations.

By way of an example, rifling characteristics of an adaptor designed forattachment to the end of the U.S. M-16 rifle in order that a BelgianSS-109 cartridge may be satisfactorily fired therefrom, will be setforth. The Belgian SS-109 cartridge is slightly longer than the standardU.S. M-16 rifle cartridge, the M-193. As noted earlier, firing a longerprojectile than originally designed to be fired from the rifle willrequire an adaptor to step up the angular velocity of the longerprojectile, which in turn is accomplished through the appropriateprogressive twist rifling within the adaptor.

Referring to Equation 1, it is possible to independently determine thequantities I_(xx), V, and D for the Belgian SS-109 cartridge. Also, theinitial and final rifling twist rates, N_(I) and N_(F), for the adaptorare obtainable. The U.S. M-16 rifle has a known barrel rifling twistrate of one turn in twelve inches. This value must be the same as theentrance rifling twist rate, N_(I), in order to facilitate transition ofthe projectile 17 from the rifle barrel 16 to the rifled cylinder 10 ofthe adaptor 11, see FIG. 5. It is also known that in order to maintaingyroscopic stability of the Belgian SS-109 cartridge, the cartridge mustexit from a rifle having a twist rate of one turn in seven inches. Thus,N_(F) must be one turn in seven inches. Substituting known values intoEquation 1 it is possible to reduce the equation to an inverserelationship between the maximum tangential force, F_(MAX) and thelength of the progressive twist rifling, L.

Through independent measurements, the maximum tangential force that theBelgian SS-109 cartridge is able to withstand may be determined. Thismaximum tangential force value has been determined to be approximately120 pounds. After selection of a peak tangential force to be applied tothe Belgian SS-109 cartridge within the adaptor, preferably some valueless than the 120 pound maximum tangential force the Belgian SS-109cartridge is able to withstand, it is possible to determine the length Lof the progressive twist rifling area. For a peak tangential force of 95pounds it is determined that the progressive twist rifling length Lwould be 3.3 inches, see FIG. 3. The instantaneous rifling twist rate Nmay then be obtained by substitution of this value for L into Equation2. The resulting instantaneous twist rate N is plotted in FIG. 3. Fromthe second equation it is also possible to calculate and plot therifling generation within the progressive twist rifling area in degrees,by selecting certain arbitrary datum points for X, see FIG. 4.

The preferred structural embodiment of the present invention has threemain elements. The first and central element is the rifled cylinder 10.The rifled cylinder 10 has an outer surface 20 and a rifled innersurface 22 as shown in FIG. 2. The rifled character of inner surface 22is more clearly shown in FIG. 2A, having lands 28 and grooves 30. Thisrifling which is produced according to known techniques, preferablyimplements Equation 2 discussed above.

Also shown in FIG. 2A is the eccentricity of inner surface 22 and outersurface 20, the inner surface having an axis 24 and the outer surfacehaving an axis 26 spaced therefrom. This slight eccentricity is one ofthree structural eccentricities which are utilized to provide asufficient degree of freedom to properly align the adaptor axis andrifling with the rifle barrel axis and rifling. Also shown in FIG. 2 isa circumferentially cut groove 40b within which set screws 36b attach tomaintain the rifled insert 10 and an outer shell 12, discussed below, ina fixed relation, see FIG. 5.

The second element of the preferred structural embodiment of the presentinvention is the adaptor ring 14 shown in a longitudinal,cross-sectional view in FIG. 6. The adaptor ring 14 has an outer surface44 and an inner surface 42. The inner surface 42 is threaded so that theadaptor ring can be connected to a rifle barrel 16 having threads on theend thereof. The adaptor ring 14 also has eccentric inner and outersurfaces as can be seen in FIG. 6A. The inner surface 42 has an axis 46and the outer surface 44 has an axis 48 slightly offset therefrom. Theadaptor ring 14 also has a circumferentially cut groove 40a similar indesign and purpose to the circumferentially cut groove 40b in the rifledcylinder 10.

The third major element of the preferred embodiment, the outer shell 12,is shown in FIG. 7. The outer shell 12 has a first bore 52 on one endthereof for receiving the rifled cylinder 10. And a second, shorterinner bore 56 on the opposite end thereof for receiving the adaptor ring14. The two inner bores 52 and 56 are designed to be axially offset andlongitudinally spaced from each other. As a result of this, the thirdand last eccentricity employed to provide a sufficient degree of freedomto properly align the adaptor axis and rifling with the rifle barrelaxis and rifling is obtained.

The outer shell 12 has an outer surface 50, an inner surface 54,associated with the first inner bore 52, and a second inner surface 58associated with the second inner bore 56. The eccentricity or axialoffset of bores 52 and 56 can be more readily seen in FIG. 7A where theaxis 62 for the first inner bore 52 is shown slightly offset from theaxis 64 for the second inner bore 56. The two bores 52 and 56 in theouter shell 12 are separated by a projecting portion 60. This projectingportion 60 is sufficiently recessed so that the projectile 17 will notcome in contact with it, as can be noted from FIG. 5. The projection 60mainly serves to provide structural integrity for the adaptor 11. Alsoshown in FIG. 7 are threaded receiving holes 38a and 38b, through whichset screws 36a and 36b are placed to engageably contactcircumferentially cut grooves 40a and 40b, respectively.

As generally illustrated in FIG. 5, the adaptor 11 may be assembled byfirst placing the rifled cylinder 10 within the first inner bore 52 ofthe outer shell 12, and secondly, by placing the adaptor ring 14 in thesecond inner bore 56 of the outer shell 12. The three elements may thenbe connected to the rifle of the barrel by threading the adaptor ring 14onto the existing threads on the end of the rifle barrel 16. In thepreferred embodiment a lock nut 15 will first be placed on the riflebarrel threads and be used to lock the adaptor assembly in place inrelation to the rifle barrel.

The axis and rifling of the rifled cylinder 10 will then be aligned withthe axis and rifling of the rifle barrel 16. Exact alignment is madepossible as a result of the above discussed three eccentricities. Therifled cylinder 10 will be rotated in relation to the outer shell 12and, after optimal alignment is obtained, fixed in position throughutilization of set screws 36b. Next, the rifled cylinder and outer shellassembly are rotated in relation to the adaptor ring 14, obtaining afurther refinement of the axial and rifle alignment. This rifledcylinder and outer shell assembly is then fixed in relation to theadaptor ring 14 through utilization of set screws 36a. Exact axial andrifle alignment is then obtained by rotation of the adaptor apparatus onthe threads on the end of the rifle barrel. Once final alignment isobtained, the lock nut 15 is moved in position to securely affix theadaptor assembly 11 in relation to the rifle barrel 16.

Also shown in FIG. 5 are threads 66 on the outer surface 20 of therifled insert 10, for accommodating a flash suppressor (not shown).

Returning to the earlier example, it will be remembered that theprogressive twist rifling area had a length L of 3.3 inches. In thepreferred embodiment of the present invention an additional increment"b", e.g. 0.2 inches, is added on each side of L to obtain a totallength "a" of the rifled cylinder 10, as shown in FIG. 2. The additionallength "b", although arbitrary, is of sufficient length so as to allowthe projectile 17 to smoothly make the transitions at the entrance andexit of the rifled cylinder 10.

Lastly, it should be noted that each of the eccentricities abovediscussed would be approximately 0.02 inches in the case of an adaptordesigned for attachment to the end of a U.S. M-16 rifle. Thiseccentricity is based upon the manufacturing parameters for the barrelof an M-16 rifle.

It will be noted that this invention fully meets the objectives setforth. A rifle adaptor is provided for attachment to the end of a riflebarrel which will provide gyroscopic stability to a projectile notoriginally designed to be fired from the rifle. Also, it will be notedthat the adaptor imparts a substantially zero entrance and exitprojectile angular acceleration and has a sufficient value therebetweento provide the required angular velocity such that the projectile isable to maintain gyroscopic stability. Additionally, it is evident thatthe three-element assembly of the present invention provides asufficient degree of freedom to allow an individual to accurately alignthe adaptor axis and rifling with the rifle barrel axis and rifling.Lastly, it will be observed that the adaptor is relatively inexpensiveand easy to construct, can be easily installed by an individual,accommodates a flash suppressor and is particularly well suited foradapting an M-16 rifle to fire SS-109 cartridges.

Although one embodiment has been illustrated in the accompanying drawingand described in the foregoing description, it will be understood thatthe invention is not limited to the embodiment discussed but is capableof numerous rearrangements, modifications, and substitutions withoutdeparting from the scope of the invention. For example, the mathematicalfunction chosen to represent the tangential force within the progressivetwist rifling area may have been a sine function or other function whichhas a value approximately zero at both ends and provides the desiredspin modification. Also, it will be observed that the three-piecepreferred structural embodiment of the present invention is onlypreferable, not necessary. It would also be possible to manufacture theadaptor of the present invention in one piece. Other changes, within thescope of the invention as defined by the appended claims, will suggestthemselves to those skilled in this art.

I claim:
 1. Apparatus for adapting a rifle to fire a projectile ofdifferent design than the rifle was manufactured to fire,comprising:first means for modifying the spin rate of a projectile firedfrom the rifle to provide gyroscopic stability to said projectile afterit exits said first means, the angular acceleration of the projectile asit exits said first means being substantially the same as the angularacceleration of the projectile as it enters said first means.
 2. Theapparatus of claim 1, further comprising:second means for attaching thefirst means to the end of the rifle.
 3. The apparatus of claim 2 whereinthe first means comprises:means for increasing the spin rate of theprojectile fired from the rifle.
 4. The apparatus of claim 3, whereinthe first means comprises:means for applying a tangential force to theprojectile within the first means, the tangential force applied to theprojectile at the entrance and exit of the first means beingapproximately zero.
 5. The apparatus of claim 4, wherein the tangentialforce has a semi-elliptically-shaped profile.
 6. The apparatus of claim4, wherein the means for applying the tangential force comprises:riflinghaving a twist rate which is a function of the longitudinal location ofthe projectile within the first means.
 7. The apparatus of claim 6,wherein the means for applying the tangential force comprises:a rifledcylinder having inner surface progressive twist rifling, said riflinghaving a twist rate which is a function of the longitudinal location ofthe projectile therein, the initial and final twist rates, and thelength of the rifled cylinder.
 8. The apparatus of claim 7, wherein therifling twist rate is in accordance with the following equation:##EQU3## where N=twist rate (inches/turn)N_(I) =initial twist rateentering the rifled cylinder N_(F) =final twist rate leaving the rifledcylinder X=projectile travel distance within the progressive twistrifling area L=length of the progressive twist rifling area of therifled cylinder ASIN=inverse sine
 9. The apparatus of claim 8, whereinthe rifle barrel has a barrel axis and exit rifling and wherein thesecond means comprises:means attaching the first means to the barrel ofthe rifle such that the barrel axis will be substantially aligned withan axis of the first means and the barrel exit rifling will besubstantially aligned with entrance rifling of the first means.
 10. Theapparatus of claim 9 for attachment to a rifle having an outer threadedsurface at the end of the rifle barrel, wherein the rifled cylinder haseccentric inner and outer surfaces and wherein the second meanscomprises:an adaptor ring, annular in shape having a threaded innersurface for engaging the outer threaded barrel surface and an outersurface eccentric to the threaded inner surface; an outer shell having:a first inner bore designed to engagably receive the rifled cylindertherein, a second inner bore eccentric to the first inner bore andaxially spaced therefrom, said inner bore being configured to engagablyreceive the adaptor ring therein, and an outer surface concentric withthe second inner bore; said rifled cylinder, adaptor ring and outershell being selectively rotatable relative to each other and to thebarrel for alignment purposes; and means for maintaining the adaptorring, outer shell and rifled cylinder in a fixed position relative toone another and relative to the rifle barrel after proper alignment ofthe apparatus with the rifle barrel.
 11. The apparatus of claim 10wherein the maintaining means comprises:a lock nut first placed on thethreaded outer surface of the barrel for securing the adaptor ring inposition relative to the outer surface of the barrel; and set screwsinserted through threaded holes in the outer shell and engaging twoshallow grooves, one groove being cut circumferentially in the outersurface of the adaptor ring, the other groove being cutcircumferentially in the outer surface of the rifled cylinder, forsecuring the adaptor ring, outer shell, and rifled cylinder in positionrelative to one another.
 12. The apparatus of claim 11 wherein therifled cylinder has an end which extends longitudinally beyond the outershell, said cylinder end having an outer threaded surface for attachmentof a flash suppressor.
 13. The apparatus of claim 12, wherein the riflecomprises a US M-16 rifle, the projectile comprises a Belgium SS-109bullet, and wherein the rifling twist rate at the entrance to the rifledcylinder is one turn in twelve inches and at the exit of the rifledcylinder is one turn in seven inches.
 14. The apparatus of claim 2,wherein the first means comprises:a rifled cylinder having eccentricinner and outer surfaces and inner surface rifling.
 15. The apparatus ofclaim 14, wherein the rifle barrel has a barrel axis and exit riflingand wherein the second means comprises:means attaching the first meansto the barrel of the rifle such that the barrel axis will besubstantially aligned with an axis of the first means and the barrelexit rifling will be substantially aligned with entrance rifling of thefirst means.
 16. The apparatus of claim 15 for attachment to a riflehaving an outer threaded surface at the end of the rifle barrel, whereinthe second means comprises:an adaptor ring, annular in shape having athreaded inner surface for engaging the outer threaded barrel surfaceand an outer surface eccentric to the threaded inner surface; an outershell having a first inner bore designed to engagably receive theadaptor ring therein, a second inner bore eccentric to the first innerbore and axially spaced therefrom, said second inner bore beingconfigured to engagably receive the first means therein, and an outersurface concentric with the first inner bore; said rifled cylinder,adaptor ring and outer shell being selectively rotatable relative toeach other and to the barrel for alignment purposes; and means formaintaining the adaptor ring, outer shell and rifled cylinder in a fixedposition relative to one another and relative to the rifle barrel afterproper alignment of the apparatus with the rifle barrel.
 17. Theapparatus of claim 16 wherein the maintaining means comprises:a lock nutfirst placed on the threaded outer surface of the barrel for securingthe adaptor ring in position relative to the outer surface of thebarrel; and set screws inserted through threaded holes in the outershell and engaging two shallow grooves, one groove being cutcircumferentially in the outer surface of the adaptor ring, the othergroove being cut circumferentially in the outer surface of the rifledcylinder, for securing the adaptor ring, outer shell, and rifledcylinder in position relative to one another.
 18. The apparatus of claim17 wherein the rifled cylinder has an end which extends longitudinallybeyond the outer shell, said cylinder end having an outer threadedsurface for attachment of a flash suppressor.
 19. The apparatus of claim18, wherein the rifle comprises a US M-16 rifle, the projectilecomprises a Belgium SS-109 bullet and wherein the rifling twist rate atthe entrance to the rifled cylinder is one turn in twelve inches and atthe exit of the rifled cylinder is one turn in seven inches.